Forecasters Caught Off Guard by Winds That Caused South Bay Outages

A hardhat sits on the ground at a Pacific Gas and Electric work site on July 30, 2014, in San Francisco. (Justin Sullivan/Getty Images)

A windstorm that caused a series of outages, knocking out power for thousands of Pacific Gas and Electric customers in Santa Clara County overnight, took local meteorologists with the National Weather Service by surprise.

High winds, with gusts reaching 54 mph, were first reported at the Monterey-area enclave of Pebble Beach Sunday evening. In the following hours, strong gusts were reported in the San Jose area and then eventually in San Francisco early Monday morning, dropping in strength as they moved north.

Those conditions did not appear in earlier computer models.

"It was definitely a big surprise," said Charles Bell, a meteorologist with the National Weather Service's Monterey office. "It was a very unusual event. We do try to forecast the best we can and certainly wish we had done a better job."

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Had the agency known in advance that such a strong event was coming, it would have publicized it, Bell said.

"We would have been sending out messages on social media. We probably would have issued a special weather statement to give people a heads up," he said. "To go from calm conditions to suddenly gusting over 50 (mph) catches people off guard and can cause problems."

While the Bay Area's winds didn't cause anything like the destruction wrought by recent hurricanes in Texas, Florida and the Caribbean, they were powerful enough to knock down trees and power lines. PG&E says electricity was out for about 11,000 customers in San Jose, Los Gatos, Campbell, Saratoga and Morgan Hill. Utility spokesman J.D. Guidi said that most of those who lost power had it restored hours later.

PG&E's meteorologists saw the wind conditions for the first time as they were happening, according to another company representative, Tamar Sarkissian.

The gusts were very isolated and difficult to predict ahead of time, Sarkissian said. The utility's weather officials described the windstorm as a low-probability, high-impact event, she said.

The conditions that led to the strong gusts may have appeared too small to be picked up in advance, according to Jan Null, a meteorologist with the private firm, Golden Gate Weather Services.

The strong gusts were the result of thunderstorms to the south that collapsed, Null said. Cold heavy air got pulled down and was spread horizontally, eventually channeled by the Santa Cruz mountains.

"This is on a scale much too small to be captured by the models," Null said.

Bell said his office plans to spend the next few days investigating how it missed the forecast.

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During that time, more unsettled weather is in the forecast. The chance of thunderstorms in the Central Coast and Bay Area is forecast to continue this afternoon into Tuesday.

Those conditions could lead to another similar wind event in the San Jose area, according to PG&E's Sarkissian.